328 Applicability of the Electric Light to Lighthouses. 



serious. It was therefore concluded that galvanic electricity is 

 not suited to the purposes of lighthouse illumination. 



Within the same period, a new mode of obtaining the 

 electric light, founded on the production of currents by mag- 

 netic induction, was tried with great success. In 1853, 

 Professor Holmes made experiments on the light obtained by 

 means of electro-magnetic machines, which had been used by 

 a Parisian company for the decomposition of water, with the 

 object of its constituents being used for combustion, but, com- 

 mercially, without success. The apparatus was imperfect; 

 nevertheless, the results were very encouraging; and they 

 became still more so when a better apparatus was used. 

 Holmes's apparatus was tried at the South Foreland lighthouse, 

 in 1859 : and its performance was favourably reported on by Mr. 

 Faraday. But, after some time, its use was discontinued there, 

 because it was considered that the light produced by it might, 

 on account of its great intensity, be visible when other lights 

 on the same coast would no longer be perceptible, through 

 foggy weather : and that vessels might thus be fatally led 

 astray. 



With a magneto-electric machine, the electricity is obtained 

 by causing soft iron, round which insulated wire has been coiled, 

 to revolve in front of one or more permanent magnets. The 

 inductive action of the permanent magnets causes temporary 

 magnetism in the electro-magnets, constituted by the soft iron 

 on which the insulated wire has been coiled. For, as the cir- 

 culation of electric currents around soft iron causes it to be 

 magnetized, so the magnetization of soft iron causes the circu- 

 lation of currents round it, and therefore in the insulated wire 

 coiled upon it. When it approaches the permanent magnet, a 

 current in one direction is generated ; and when it recedes from 

 it, and returns to its natural state, a current in the opposite 

 direction. A very simple contrivance, called a commutator, 

 causes both currents to proceed in the same direction, and 

 therefore to produce a combined effect : and these currents may 

 be called into existence so rapidly, as ■ to render the light 

 emitted by them, so far as our senses are concerned, continuous 

 and uniform. 



It is obvious that the production of light, in this way, is 

 merely an example of the correllation of the physical forces, 

 and of a change of the imponderables, successively, one into 

 the other. Luminous calorific and actinic rays, emitted by the 

 sun — it cannot ever be conjectured how long ago — were ab- 

 sorbed by the vegetable which gave rise to the coal : these, in the 

 furnace of the steam boiler, are liberated in the form of heat : 

 this heat is changed by the steam-engine into motion : this 

 motion is changed into electricity by the magnet : and this 



